Surrounding SN 1987A is a three-ring nebula attributed to interacting stellar winds , yet no model has successfully reproduced this system .
Fortunately , the progenitor ’ s mass-loss history can be reconstructed using light echoes , in which scattered light from the supernova traces the three-dimensional morphology of its circumstellar dust .
In this paper , we construct and analyze the most complete map to date of the progenitor ’ s circumstellar environment , using ground and space-based imaging from the past 16 years .
PSF-matched difference-imaging analyses of data from 1988 through 1997 reveal material between 1 and 28 ly from the SN .
Previously-known structures , such as an inner hourglass , Napoleon ’ s Hat , and a contact discontinuity , are probed in greater spatial detail than before .
Previously-unknown features are also discovered , such as a southern counterpart to Napoleon ’ s Hat .
Careful analyses of these echoes allows the reconstruction of the probable circumstellar environment , revealing a richly-structured bipolar nebula .
An outer , double-lobed “ Peanut , ” which is believed to be the contact discontinuity between red supergiant and main sequence winds , is a prolate shell extending 28 ly along the poles and 11 ly near the equator .
Napoleon ’ s Hat , previously believed to be an independent structure , is the waist of this Peanut , which is pinched to a radius of 6 ly .
Interior to this is a cylindrical hourglass , 1 ly in radius and 4 ly long , which connects to the Peanut by a thick equatorial disk .
The nebulae are inclined 41°south and 8°east of the line of sight , slightly elliptical in cross section , and marginally offset west of the SN .
From the hourglass to the large , bipolar lobes , echo fluxes suggest that the gas density drops from 1–3 cm ^ { -3 } to \gtrsim 0.03 cm ^ { -3 } , while the maximum dust-grain size increases from \sim 0.2 \mu m to 2 \mu m , and the silicate : carbonaceous dust ratio decreases .
The nebulae have a total mass of \sim 1.7 M _ { \sun } .
The geometry of the three rings is studied , suggesting the northern and southern rings are located 1.3 and 1.0 ly from the SN , while the equatorial ring is elliptical ( b / a \lesssim 0.98 ) , and spatially offset in the same direction as the hourglass .